In a memory cell consisted of a single transistor and a single capacitor, a discharge of the capacitor makes the stored information therein be destroyed and erased. Therefore, the periodical rewriting of the information, called the refreshing operation, is necessary to continuously store the information. The semiconductor device requiring refreshing operation has a memory control circuit, to perform regular refreshing operations, to perform regular refreshing operations at certain time intervals.
FIG. 1 is a system block diagram of the conventional semiconductor memory device performing refreshing operations. The semiconductor device of FIG. 1 uses DRAM as a memory device 100. If the memory device 100 is internally provided with a refresh address generator 80, the refresh address generator 80, shown in the dotted lines, is not needed.
The refreshing operations are regularly and within a certain time interval carried out through signals produced, by various components such as a central processing unit (CPU) 60 for controlling the memory device 100, an address selector 70, a timer and controller 90, and a refresh address generator 80. Generally the time intervals of the refreshing operations, in a dynamic RAM of 1 mega bits, is 8 msec, and this is executed in 512 cycles.
If it is assumed that 2048 cells are connected to a row address, then all the cells of 1 mega bits can be refreshed, i.e., 512.times.2048=1,048,576 bits. The range of the refreshing operation is determined in dependence upon the refresh characteristics of the semiconductor memory device, and usually, the refresh characteristics at the room temperature (25.degree. C.) are better by about 10 times than that at a high temperature (83.degree. C). However, the range of the refreshing operation is determined by the high temperature refresh characteristics. Therefore, the refreshing operation at room temperature accompany the unnecessary refreshing operations, with the undesirable result that the power consumption is increased, and that the input/output operations of data are restricted by the refreshing operation time.